NATO is testing its ability to rapidly deploy across eastern Europe – without direct U.S. assistance – as Washington shifts its approach toward European defense and the war in Ukraine. The six-week Steadfast Dart 2025 exercises across Bulgaria, Romania and Greece are taking place as Russia´s invasion of Ukraine approaches the three-year mark. They involve some 10,000 troops from nine nations and represent the largest NATO operation planned this year. The U.S. absence from the exercises comes as European nations scramble to build greater military self-sufficiency over their concerns about the Trump administration´s commitment to common defense and demands for increased European military spending. President Donald Trump on Wednesday announced his intention to negotiate with Russia directly. And U.S. Defense Secretary Pete Hegseth said at his first meeting with NATO colleagues in Brussels on Wednesday that European nations should dramatically increase their defense spending and shoulder the “overwhelming share” of funding for Ukraine. Greek and Spanish marines are leading Thursday´s military demonstration, an amphibious assault, near the central Greek city of Volos, marking the first full-scale operational deployment of NATO´s new Allied Reaction Force. The force, established last July, represents NATO´s latest strategic evolution, designed to deploy at scale within 10 days, combining conventional forces with cyber and space-based technologies. Western military officials – anticipating lasting tension with Russia and President Vladimir Putin, possibly beyond the Ukraine conflict – argue that NATO´s new capability is becoming increasingly important to reinforce its eastern flank. “We now realize that the world we thought would exist has almost disappeared,” Greek Defense Minister Nikos Dendias told a security conference in Washington this week. “These challenges cannot be addressed by individual nations, not even by a nation as mighty as the United States.” The current exercise involves forces from nine NATO members, including regional rivals Greece and Turkey, deploying 17 naval vessels, more than 20 aircraft and over 1,500 military vehicles. Britain leads the operation with 2,600 military personnel and 730 vehicles, assuming command of all land forces during the drills. “Exercise Steadfast Dart demonstrates our unshakeable commitment to NATO and highlights the U.K.´s key leadership role in the alliance,” said Luke Pollard, a British deputy minister for defense, ahead of the exercise. “As we approach the three-year anniversary of Russia´s illegal full-scale invasion of Ukraine, we must continue to strengthen our collective defenses together to deter Putin effectively.” The drills, which end Feb. 26, focus on rapid deployment scenarios and multi-domain operations across air, land, sea and special forces, underscoring NATO´s shifting military posture along its eastern boundaries. Participating nations are Bulgaria, France, Greece, Italy, Romania, Slovenia, Spain, Turkey and the United Kingdom. Earlier this week, Communist-backed groups staged small protests near the training area in central Greece, opposing the country´s involvement in overseas deployments.